Sheet feeding apparatus having mechanisms for supporting, separating and advancing single sheets in seriatim are most commonly used in the printing, recording and copying fields.
It is well known that the separation and seriatim advancing of sheets from a stack or pile of sheets presents many problems due to the differences in size, weight, stiffness and surface characteristics of the sheets. Moreover, the characteristics of the sheets will vary depending upon humidity and electrostatic conditions.
Various types of sheet feeding systems have heretofore been utilized in the printing, recording and copying fields, such as the following which have been summarized in U.S. Pat. No. 3,861,670 issued on Jan. 21, 1975 to William A Kraft:
A system that utilizes feed rollers mounted pivotably and biased into engagement with an uppermost sheet of a stack of sheets. The feed rollers cooperate with drag pads engaging a side edge of the stack to insure that only the uppermost sheet is fed from the stack; PA1 a system that utilizes feed rollers pivoted into engagement with an uppermost sheet of a stack and snubbers securing the leading edge of the stack; PA1 a system that utilizes vacuum feed arms or adhesive rollers operating in conjunction with an elevating sheet tray to pick up a top sheet from a stack of sheets and advance it into a set of feed rollers; and PA1 a system that utilizes a stationary feed roller cooperating with a retard roller, biased into engagement therewith or spaced therefrom, and a nudger roller or endless belt that is biased against an uppermost sheet of a stack of sheets.
The disadvantages of the above systems, as respectively stated in the Kraft patent, are that they rely heavily upon sheet strength, sheet stiffness, sheet weight and approach angle to the feed nip which, if not consistent, may mar or notch the paper.
While the Kraft patent claims to have overcome the disadvantages of the prior art, a disadvantage of the Kraft system is the lack of a simple copy sheet aligning feature.
In U.S. Pat. No. 4,426,150, issued on Jan. 17, 1984 to Hiroshi Matsumoto and Tomoki Ogura, there is disclosed an original document feed and aligning apparatus having an incline roller for guiding an original document, both toward a stop lever and along a lateral edge of the apparatus for in-track, cross track and skew alignment. Nowhere in this patent, however, is there any disclosure of a means for preventing multiple feeding of the original document. In addition, the feeding and alignment system is complex, requiring many interconnecting gears and shafts to accomplish alignment.
From the above, it is apparent that numerous approaches have been attempted to obtain reliable separation and seriatim advancing of a sheet from a stack of sheets. However, none of the approaches combines a sheet aligning system for cross-track, in-track and skew alignment that is simple and reliable with a practical means for preventing multiple sheet feeds.